Electronic photocopying apparatus and method



Aug. 25, 1964 A. L. KAUFMAN ELECTRONIC PHOTOCOPYING APPARATUS AND METHODFiled Jan, 26, 1960 I NV EN TOR.

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United States Patent O ce 3,146,100 ELECTRONIC PHOTOCOPYING APPARATUSAND METHOD Arthur L. Kaufman, Westport, Conn., assigner to Bohn BusinessMachines, Inc., a corporation of New York Filed Jan. 26, 1960, Ser. No.4,737 3 Claims. (Cl. 96-1) This invention pertains to methods andapparatus for rapidly reproducing duplicates of letters, printed ortyped sheets, or sheets having thereon a pattern of any characterforming areas of differing light reflectivity.

According to a feature of the invention, reproduction in accordancetherewith is effected in a matter of seconds in a continuous, completelydry state process requiring no special skill or training by theoperator, in contrast to the many duplicating processes heretofore knowninvolving wet treatments and/or treatments conducted in successive anddistinct stages, such as are required in photographic processes and thelike, and which are time-consuming and require some considerable degreeof special operative knowledge and skill.

According to another feature, the duplicates produced according to theinvention are of a permanent character unaffected by exposure to heat,light or passage of time, such as are inherent in duplicates produced byvarious known means and procedures.

In accordance with the invention, duplicates of a master copy areproduced on sheet stock, of paper for example, coated on one side with alight sensitive medium, such as Zinc oxide or the like, by firstimpressing thereon a substantially uniform electrostatic potentialextending throughout the surface area thereof, and thence variablydischarging the same in accordance with a light contrasting pattern onthe master, by means of light reflected from the master and focused ontothe coated sheet stock to produce a latent electrostatic image thereon,following which the so-treated duplicate sheet stock is contacted with afinely divided admixture of iron or other magnetic particles andparticles of a thermosetting resin while maintaining the admixture underthe influence of a magnetic field.

' As a consequence the resin particles are deposited onto theduplicating sheet stock in accordance with the latent electrostaticimage pattern formed thereon as above, the resin deposit beingthereafter set by heating to convert the resin to the thermosetcondition adherently bonded to the sheet stock. Ordinarily a resinincorporating a pigment, usually black, is employed for such purposesthus to produce a pattern in black on the coated sheet stock. The resinparticles are electrically charged by means of the triboelectric effectby contact with the particles of magnetic material, the resin particlesbeing preferably more finely comminuted than the magnetic particleswhereby a relatively large number of the former adhere to each magneticparticle.

In duplicates as thus produced, there is in some instances a tendencyfor an appreciable amount of the resin particles to be retained inbackground areas, which is objectionable. This results from the factthat the zinc oxide coated surface of the duplicating sheet stock has arather rough surface microscopically, often causing substantial amountsof the resin dust mechanically to adhere to background areas; and alsofrom the further fact that the charging potential initially impressed onthe coated surface may not be completely discharged from the backgroundareas during the reproducing procedure.

In accordance with a feature of my invention, in its preferredembodiment, I eliminate this defect by exposing the duplicate sheetafter the resin pattern is formed thereon in the manner aforesaid butprior to heat-setting 3,146,100 Patented Aug. 25, 1964 the same, to asource of light for uniformly exposing all areas of the duplicate sheetstock, thus fully to discharge all residual potentials retained onbackground areas. The printed or patterned areas are substantiallyunaffected by this treatment owing to the opacity of the resin contentdeposited on these areas. Following this uniform light exposure, Icontact the sheet with a layer of iron or other magnetic particlesmaintained in a magnetic tield, whereby the resin particles of thebackground areas are withdrawn thus leaving a clear background surface.Although some resin content is also thus withdrawn from the patterned orprinted areas, the initial deposition layer thereof is sufficientlyheavy that the reproduction is substantially unaffected.

Having thus described my invention in general terms,

reference now will be had to the accompanying drawings for a moredetailed description of a preferred embodiment of a method and apparatusfor practicing the same wherein:

FIG. l is a schematic View in perspective and partially in section ofthe essential apparatus employed as explained below; while FIG. 2 is asection of a component of the FIG. l apparatus as taken at 2-2 thereof.FIGS. 3, 4 and 5 are, respectively, plan view of, a master sheetembodying a pattern to be reproduced, a view of the duplicate sheet atan intermediate stage of my preferred process, and a view of the nishedduplicate sheet.

Referring to FIG. 1, the master sheet 10, having indicia 11 thereon,such as typed or printed matter, a drawing or other pattern to bereproduced, is progressively fed horizontally between pairs of pinchrolls 12, past a light and reflector source 13 for brightly illuminatingthe same. At the same time the duplicating sheet stock 14, is fed at thesame lineal speed in the form of continuous strip, from a roll thereof(not shown), thence under a guide roll 15, and thence vertically upwardbetween pairs of spaced electrodes in the form of flamentary pairs ofwires 16, 17, disposed respectively on opposite sides of the path ofstrip travel as shown. The wires 16 are connected together as shown andconnected thence over a lead 18 to the positive output terminal of astep-up transformer and rectifier unit 19, having an input plug-inconnection 20 for connection to an A C. power source, such as theconventional 60 cycle, 110 volt building power supply. The wires 17 onthe opposite side of the strip travel and which face the coated surface25 of the sheet stock 14, are also connected together as shown andconnected thence over a lead 21 to the negative output terminal of unit19.

In a physical embodiment of the invention which has been operatedsuccessfully, the wire pairs 16 and 17 are spaced about 1/2 inch onopposite sides of the path of strip travel, and a direct current voltageof about 6000 volts is impressed between them from unit 19, this voltagebeing such as to produce a slight corona effect along each of the wires16, 17. These wire pairs are, respectively, housed in metal shields 22,23, grounded as at 24, for protective purposes. The sheet stock 14, iscoated on the exposed surface shown with a zinc oxide or equivalentelectrical insulative, light sensitive coating, as at 25. As aconsequence, as the stock is fed between the energized electrode pairs16, 17, the coated surface is charged throughout to a substantiallyuniform negative potential with respect to ground.

For purposes of reproducing by electrostatic potential variation on thethus charged stock, the indicia or pattern 11 on the master sheet 10, anoptical scanning and focusing system is provided. This comprises amirror 30, a convex focusing lens 31, and a mask 32, having a narrow,slotted aperture 33 formed therein. The mask is mounted, as shown,adjacent the path of travel of the sheet stock 14 and facing its coatedsurface 25, with the slotted aperture 33 extending transversely thereof.The mirror and lens are so disposed as shown that light reflected fromthe surface of the master 10, is picked up by the mirror and reflectedthence at right angles through the lens and onto the area of the sheetstock 14 which is covered by the mask 32 except for the slotted aperture33 therein, the mask being of sufficient height and width to block offall light thus reflected except for the narrow beam 34 which passesthrough the slotted aperture 33. The lens is so positioned that the beamis brought to a focus on the coated surface of the sheet stock 14, thusforming thereat an optical image corresponding to an exposure area 35 ofthe master 10.

Accordingly, as the master is fed in the direction of the arrow, theexposure area 35 will in effect sweep along the master in the oppositedirection and thus progressively scan the master from end to end.Similarly, the light reected from the master within the exposure areawill be reflected and focused by the optical system through the slot ofthe mask onto the coated surface of the duplicating stock which is beingfed at the same lineal speed as the master, and thus progressivelyreproduce therealong an optical image of the exposure area of the masterfrom instant to instant, thereby variably to discharge the electrostaticpotential on the duplicating stock in accordance With said image. Inthis way the indicia or pattern on the master is reproduced as a latentelectrostatic image on the coated surface of the -duplicating stock.

Referring to FIGS. l and 2, the stock is fed past the masking member 32from a guide roll 39 and thence over a guide roll 40 across atransversely extending slot 41 formed in a tubular member 42 housing adrum 43, and thence under a guide roll 43a, the housing and drum beingmade of a non-magnetic material, such as polyethylene, or other suitablesynthetic resin. Integral with the drum, are oppositely extending shaftportions 44, 45, rotatable in bearings 46, 47, on which are respectivelymounted, end plates 49, 50, which close off the opposite endsrespectively of the housing 42.

Embedded in the drum are a series of radially extending bar typepermanent magnets, as at 51, disposed equiangularly thereabout, as shownin FIG. 1, and equi-spaced therealong, as shown in FIG. 2. The outerends of the bar magnets are all of like polarity. Disposed about thedrum 43 and within the housing 42, is a layer 52 comprising a finelycomminuted admixture of iron particles and particles of a thermosettingsynthetic resin, such as a phenolformaldehyde or equivalent resin, inthe thermosetting stage of cure. The resin preferably incorporates ablack pigment, to produce a black on white pattern on the duplicatingstock.

Due to the triboelectric effect, the resin particles electrostaticallyadhere to the iron particles, and the admixture assumes an upstandingtufted or feather duster configuration over each bar magnet, as at 53,under the inuence of the magnetic fields extending radially outward fromthe respective bar magnets 51. The guide rolls 4f), 43a so space thepath of travel of the duplicating stock 14 from the drum 43, that as theduplicating stock is fed over the slot 41 in the housing 42, its coatedsurface contacts the outer ends of the tufted masses 53, during whichtime the drum 43 is rotated by shaft 44 in the opposite direction tothat of the strip feed. As a result, the positively charged resinparticles are withdrawn from the resin-iron admixture, by the negativeelectrostatic potential on the strip 14, and deposited on the coatedsurface in amounts varying from point to point in accordance with thecorresponding variation in electrical potential thereon.

Only residual amounts of resin particles will be deposited on thebackground areas of the duplicating stock corresponding to thebackground areas of the master, since the potential in those areas willhave been substantially discharged by the light reflected from themaster onto such areas. On the other hand, the resin particles will bedeposited in relatively heavy layers throughout areas of the duplicatingstock corresponding to the pattern i areas of the master, since littlelight will have been reflected therefrom to discharge the potential ofcorresponding areas of the duplicate. The thickness of resin layerdeposits on these pattern areas will of course vary from point to pointwith the amount of light reflected from the master at correspondingpoints.

As above stated, duplicating stock is fed past slot 41 from the guideroll and thence under the guide roll 43a. At this stage there has beenreproduced on its coated surface, a pattern composed of the depositedresin particles corresponding to that of the master with some sprinklingof resin particles also deposited in the nonpatterned or backgroundareas. Thus referring to FIGS. 3 and 4, if we assume the master 56comprises the large block letter T printed in solid black on whitepaper, the reproduction thereof on the duplicating stock 14 as it passesunder the guide roll 55, would be about as shown in FIG. 3. That is, theblock letter T of the master 56 will be faithfully reproduced in blackon the duplicating stock as at 57, but the background area 58 of theduplicate, will not in general be pure white, as at 59 of the master,but will ordinarily have the somewhat mottled appearance shown at 58,owing to adhering resin particles or small masses thereof, as at 60.These are deposited as above stated as a result of the rather coarsecoated surface of the duplicating stock and also by residual amounts ofelectrical potential retained on discrete areas thereof.

In order to remove these background resin deposits, the stock 14 is fedfrom guide roll 43a, past a lamp and reflector element 65 of sufficientintensity completely to discharge residual background area potentials,the patterned or printed areas, however, remaining substantiallyunaffected by the opacity of the resin deposit thereon. The strip is fedthence across the slot 66 in a housing 67, enclosing a permanent magnetbearing drum 68 constructed like that above described, but which isenveloped in a layer of finely divided iron particles 69, which assumesthe tufted configuration shown owing to the magnetic fields abovediscussed. This drum is likewise oppositely driven to the direction ofthe strip feed, contact between the paper stock and the tufts of ironfilings serving to withdraw the resin particles from the backgroundareas of the duplicating stock.

The strop is fed beyond the drum 63, under a guide roll 70. At thisstage the pattern on the duplicating stock has the appearance shown inFIG. 5, with both the block letter T and the background area beingfaithfully reproduced as in FIG. 1, the resin particles of FIG. 4 havingbeen removed in the manner aforesaid.

At this stage the resin deposit on the pattern areas is held against thestock only by electrostatic attraction and can be rubbed olf. In orderpermanently to bond the deposited resin pattern to the stock, it is fedover an electrical heating coil 71, which fuses the resin into a solid,fully cured thermoset state, adherently bonded to the sheet stock.

What is claimed is:

l. The method of reproducing on a duplicating sheet of material coatedwith a photoconductive insulating medium, a contrasting pattern formedon a master sheet by areas having different degrees of light absorption,which comprises: progressively feeding said duplicating sheet betweenspaced electrodes having a high direct current voltage impressedtherebetween for charging all so-coated areas of said duplicating sheetto a substantially uniform electrostatic potential, concurrentlytherewith progressively feeding said master sheet past a source ofillumination, while focusing a beam of rays reflected from said masteronto said duplicating sheet thereby to discharge the potential fromareas thereof in accordance with the pattern on said master, feedingsaid duplicating sheet thence in progressive contact with a magneticallysuspended rotating substantially cylindrical mass composed of anintimate admixture of particles of magnetic material and particles of asubstantially opaque thermosetting synthetic resin in a ine state ofsub-division, said mass being suspended in a magnetic field extendingradially from the surface thereof and directed substantially normal tothe path of travel of said duplicating sheet, whereby said resinparticles are deposited on said sheet in accordance with theelectrostatic potential pattern thereon, thus to reproduce thereon thepattern on said master sheet, feeding said duplicating sheet thence pasta light source having suicient intensity to discharge therefrom residualpotentials retained on background areas thereof, but prevented by theopaqueness of said resin particle from substantially discharging theresidual potentials retained on the image areas thereof, and thence incontact with a magnetically suspended substantially cylindrical masscomposed of particles of a magnetic material in a fine state ofsub-division, said mass being suspended in a magnetic field extendingradially outward from the surface thereof and directed substantiallynormal to the path of travel of said duplicating sheet, thereby toWithdraw therefrom resin particles adhering to said background areas,and feeding said duplicating sheet thence past a source of heat forconverting the resin pattern thereon to the thermoset conditionadherently bonded to said sheet.

2. The method of duplicating on a photoconductive surface, a lightcontrasting pattern from the surface of a master, said methodcomprising: impressing a uniform electrostatic potential on andthroughout said photoconductive insulating surface, focusing thereon animage from the surface of said master by light projected therefrom,thereby to produce on said photoconductive-insulating surface anelectrostatic image of the pattern on the master surface, thereaftercontacting the electrostatically imaged photoconductive insulatingsurface with finely comminuted particles of a substantially opaque resinto deposit such particles thereon in accordance with said electrostaticimage, uniformly illuminating the so treated photoconductive insulatingsurface with an illuminating intensity sucient to discharge residualelectrostatic potentials throughout the background areas of said patternbut substantially insuicient to discharge the electrostatic potentialthroughout the image areas of said pattern, and brushing evenly acrossthe entire photoconductive insulating surface bearing said depositedresin particles to remove residual resin particle deposits from saidbackground areas.

3. The method of reproducing on a duplicating sheet of material coatedwith a photoconductive insulating medium, a light contrasting patternformed on a master sheet by areas having different degrees of lightreflection which comprises: progressively feeding said duplicating sheetbetween spaced electrodes having a high direct current voltage impressedtherebetween for charging all so-coated areas of said duplicating sheetto a substantially uniform electrostatic potential, concurrentlytherewith progressively feeding said mastersheet past a source ofillumination while focusing a beam of rays reected from said master ontosaid duplicating sheet thereby to discharge the electrostatic potentialfrom areas thereof in accordance with the pattern on said`\master,feeding said duplicating sheet thence in progressive contact with a massof particles of a substantially opaque thermosetting resin in a finestate of subdivision, whereby the resin particles are deposited on thesheet in accordance with the electrostatic potential thereon, thus toproduce thereon the pattern on said master sheet, feeding saidduplicating sheet past a light source having sufficient intensity todischarge therefrom residual potentials retained on background areasthereof, but prevented by the opaqueness of said resin particles fromsubstantially discharging the potentials retained on the image areasthereof, and thence brushing evenly across the entire surface of fsaidduplicating sheet so as to withdraw therefrom resin particles adheringto said background areas.

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1. THE METHOD OF REPRODUCING ON A DUPLICATING SHEET OF MATERIAL COATEDWITH A PHOTOCONDUCTIVE INSULATING MEDIUM, A CONTRASTING PATTERN FORMEDON A MASTER SHEET BY AREAS HAVING DIFFERENT DEGREES OF LIGHT ABSORPTION,WHICH COMPRISES: PROGRESSIVELY FEEDING SAID DUPLICATING SHEET BETWEENSPACED ELECTRODES HAVING A HIGH DIRECT CURRENT VOLTAGE IMPRESSEDTHEREBETWEEN FOR CHARGING ALL SO-COATED AREAS OF SAID DULPLICATING SHEETTO A SUBSTANTIALLY UNIFORM ELECTROSTATIC POTENTIAL, CONCURRENTLYTHEREWITH PROGRESSIVELY FEEDING SAID MASTER SHEET PAST A SOURCE OFILLUMINATION, WHILE FOCUSING A BEAM OF RAYS REFLECTED FROM SAID MASTERONTO SAID DUPLICATING SHEET THEREBY TO DISCHARGE THE POTENTIAL FROMAREAS THEREOF IN ACCORDANCE WITH THE PATTERN ON SAID MASTER, FEEDINGSAID DUPLICATING SHEET THENCE IN PROGRESSIVE CONTACT WITH A MAGNETICALLYSUSPENDED ROTATING SUBSTANTIALLY CYLINDRICAL MASS COMPOSED OF ANINTIMATE ADMIXTURE OF PARTICLES OF MAGNETIC MATERIAL AND PARTICLES OF ASUBSTANTIALLY OPAQUE THERMOSETTING SYNTHETIC RESIN IN A FINE STATE OFSUB-DIVISION, SAID MASS BEING SUSPENDED IN A MAGNETIC FIELD EXTENDINGRADIALLY FROM THE SURFACE THEREOF AND DIRECTED SUBSTANTIALLY NORMAL TOTHE PATH OF TRAVEL OF SAID DUPLICATING SHEET,